1. Field of the Invention
The present invention relates to guide wires used in medical procedures to gain access to specific areas of the body without major surgery. More specifically, the present invention deals with a flexible guide wire having a controllable stiffness.
2. Description of Related Art
Medical catheters generally comprise elongate tube-like members that may be inserted into the body, either percutaneously or via a body orifice, for any of a wide variety of diagnostic and interventional purposes. Such catheters are particularly useful with regard to certain cardiovascular applications where the object is to deliver a treatment or instrument to a remote lesion. Often, the instrument must cross a lesion consisting of hard and inflexible tissue having a very rough surface or even protruding flaps. For example, Percutaneous Transluminal Coronary Angioplasty (PTCA or balloon angioplasty) requires manipulation of a catheter through extended portions of the patient's arterial system to the stenotic site for the purposes of alleviating the lesion by inflating a balloon.
A PTCA guide wire is typically a long, flexible wire, coiled or uncoiled, having one or more components. The guide wire is generally used to gain access to a body structure or location by inserting it transluminally into the brachial or femoral artery and then advancing it to the desired location. The guide wire can be used to probe, biopsy, penetrate, dilate, or act as a vehicle for transporting an accompanying catheter to a given location. PTCA procedures generally require a guide wire flexible enough to go around bends and yet stiff enough to be pushable and capable of driving through the arterial blockage. Thus, the goal in designing a guide wire is to design a flexible and directable guide wire still capable of pushing through blockage at the stenotic site.
Coronary arteries, however, are circuitous and/or tortuous and have many sub-branches. Often, the stenotic region is located where the diameter of the artery is small, or, by its very presence, the stenotic region leaves only a very small opening through which a guide wire can pass. Effective steering of the tip and/or body of the guide wire becomes very important for the quick, safe, and accurate passage and placement of the guide wire preceding the transport and positioning of a PTCA catheter. Thus, guide wires have often been provided with flexible distal tips. The flexible tip allows the cardiologist to pre-bend the distal tip of the guide wire before insertion and then rotate (or torque) the guide wire once it has reached a branch artery to enable the bent tip to enter the branch. Typically, the very distal 1 cm. of the guide wire is bent into a J-shape of approximately 5-10 mm. Note that a cardiologist is not limited to a J-shape and may choose any shape that will be helpful in directing the guide wire to negotiate turns.
The cardiologist encounters several difficulties in attempting to rotate the prebent guide wire into the desired position. For example, particular difficulty is met with pre-bending in cases where an artery branches at a first angle and then sub-branches at a second angle. As a result, if the cardiologist is unable to enter the desired arterial branch through rotation of the guide wire, the pre-bent tip may need to be adjusted. If adjustment is required, the guide wire is removed, re-bent, and reinserted, often multiple times during a single procedure. With repeated removal and reinsertion of the guide wire, the procedure is accompanied by the risk of significant trauma to the arterial lining, and in many cases, the obstruction cannot be reached at all. The necessity of repeatedly removing and adjusting the guide wire also increases the time and cost associated with each procedure. Further, rotation of the distal end of the guide wire typically lags behind rotation of the proximal end of the wire (i.e., the control end), such that precise rotational control by the cardiologist is difficult, if at all possible. Friction in the arteries can cause the distal end to rotate in a jerky fashion, rather than a slow consistent motion, which can traumatize the vascular intima and also interfere with the rotational control. Any one or combination of these issues may prevent the cardiologist from successfully directing the guide wire into the desired arterial branch.
In an effort to address the above difficulties, guide wires have often been provided with a stiffer distal extremity (tip) in order to achieve the stiffness required to place a stent in the desired location. However, when such a guide wire employs a stiff distal tip, it is difficult for the guide wire to initially enter the vessel and negotiate tortuous sites encountered in the vessel. Thus, it is generally preferred for the tips of guide wires to be floppy at entry. These conflicting yet essential characteristics of a functional guide wire have often made it necessary to utilize two separate guide wires in a single procedure. A guide wire having a floppy distal extremity for directing the wire into the desired location through the arterial branches is inserted first. The floppy guide wire is then replaced by a second guide wire having a stiffer distal tip for actually positioning the catheter in the desired location.
A variety of constructions have been proposed to provide guide wires steerable from the proximal end that still allow the guide wire to be advanced through non-linear cavities without removal for adjustments or the use of a separate additional guide wire. These constructions include shape memory alloy devices that when heated change orientation, and devices employing wires or pulleys to steer the tip from a handle located outside the body. However, each of these devices has significant limitations.
Shape memory alloy devices are devices whose shape changes as the device is heated or cooled. For example, a device may initially have a small J-shape, but when heated develops a larger more defined J-shape. The heating of a shape memory alloy device may be provided by a change in body temperature (i.e., the guide wire is inserted further into the body) or through resistance heating. When using resistance heating, the guide wire core contains one or more wires through which a current is supplied to the tip of the guide wire. Actuators are coupled to the wire(s) to supply the current, and multiple actuators can be used to further vary the movement or developing shape of the guide wire's distal tip. However, such devices are very expensive, and typical guide wire constraints allow limited space for the actuating element(s). Not only do shape memory alloy devices possess cost and size restraints, they also often have a slow response time due to their reliance on heat transfer as the operative control mechanism.
Guide wires using pulley systems have been developed having filaments that run through the core of the guide wire. The filaments are manipulated, often through use of a joystick, to control the orientation of the distal tip. Such devices have problems achieving control over long distances, since long small diameter wires requiring only minimal changes in length to actuate do not afford very precise control. In addition, the cable tension required for such devices to work effectively dictates that the stiffness of the tip, which is critical to device effectiveness, be altered by an actuating mechanism. The overall size of the device trades off against the ability to tension the cable, where the strain in the tensioned cable increases as device size decreases.
In addition to limited steerability, both types of prior art guide wires rely on the spring tension of the guide wire coil to return the guide wire to a straight, unbent position. However, straightening the wire after negotiating the branch is as important as deflecting the wire for entry into a branch artery. Any ability to straighten prior art devices described above is from spring tension or other structures in the distal end of the wire, both of which serve to compromise the desired floppiness of the guide wire tip.
Thus, it is desirable to provide a readily insertable guide wire that is also accurately steerable. Effective control over tip or body deflection and stiffness of the wire, which provides the necessary steering capability, is important so that the guide wire can be quickly and accurately steered and guided through a desired path to the desired location within the body. It is desirable to achieve a remotely steerable catheterization device that does not incur the penalties of stiffness, precision, or size currently associated with the prior art devices.